The 26-year-old Sobotka injured his left leg playing for the St. Louis Blues in a 3-1 loss to the Carolina Hurricanes on Friday. The Blues said he would not recover from the injury in time for the Olympic tournament.
Sobotka had seven goals and a total of 25 points from 46 games this season.
Czech coach Alois Hadamczik announced the replacement Tuesday, recalling Erat for his third Olympics.
The 32-year-old right wing helped the Czechs win the bronze medal at Turin in 2006.
The Czechs open the tournament Feb. 12 against Sweden and also face Latvia and Switzerland in Group C.